1. Field of the Invention
The invention relates to an amplifier circuit, and more particularly to an amplifier circuit with an overshoot suppress scheme.
2. Description of Related Art
In the signal process and control system, the amplifier circuit is usually used to adjust, transmit, enhance, or reduce signals. The amplifier has a plurality of types. According to the application and the bandwidth requirement of the used amplifier, it can be divided into the power amplifier, the tuning amplifier, the input stage amplifier, and the output stage amplifier.
For the conventional amplifier, when it outputs the output signal, the overshoot may occur in the output signal during the dynamic operation due to the phase margin, the insufficient area, and so on. The overshoot represents that, in the circuit, the transient instant voltage can not be immediately stabilized and is much greater than the steady voltage during the period of the converting state. When the signal is outputted, it will cause the signal to be unstable. Accordingly, the back circuit to receive the signal may operate abnormally, and even the circuit is burned out. However, in many applications, a steady output voltage is needed, and the problem that the voltage is raised in a very short time must be suppressed within a tolerable scope.
In the prior art, by designing a larger phase margin, the dynamic response becomes slower to suppress the overshoot, and for different conditions, such as the process, the voltage, and the process-voltage-temperature variation (PVT variation), the phase margins in different conditions are much different, so that it is required to change the design of the circuit according to different conditions. Other methods, such as the method of speeding the change of the transient state by increasing the current, or the method of adding capacitors in the output end to reduce the amplitude of the oscillation and stabilize the output voltage, also increase the fabricating coat and the circuit area.